Dont know about none oem but I have the oem for my R12R 18'. They are really good quality as you'd expect from bmw. They are made of a nylon/neoprene type matierial , this does make them a little thick but they are moulded so they fit the panniers perfectly.
Most of the others available are nylon denier material so are more bag like and don't hold there shape as well.
Most of the others available are nylon denier material so are more bag like and don't hold there shape as well.